This invention relates generally to memories using chalcogenide materials.
Chalcogenide materials have been used as semiconductor memories for a number of years. These memories may be traditionally referred to as phase change memories. They typically involve the change from an amorphous to a crystalline phase. Chalcogenide memories to date have used materials that are bi-stable in that they will change from a generally amorphous state to a generally crystalline state when exposed to 200° C. for 30 minutes or less, and back to amorphous state by application of 650° C. for brief time with a rapid quench.
One advantage of chalcogenide materials in semiconductor memory applications is that a relatively modest amount of heat may transition the devices between different detectable phases or states. This heat may be generated by applying a current or voltage to the chalcogenide material.
While phase change materials have many advantages, they may also have some disadvantages in some situations. For example, the “off” state leakage may be high. An ovonic threshold switch has been viewed as a single-state chalcogenide device, but with a high “off” state leakage. When combined in series with a two state chalcogenide material, a high “off” state leakage results and with a two state memory. However, the resulting two layer stack requires multiple depositions.